1. Field of the Invention
The invention relates to an adaptive antenna receiving apparatus, and more particularly to an adaptive antenna receiving apparatus which is capable of rapidly carrying out adaptive convergence by virtue of an initial weight close to a convergent value of adaptive weight.
2. Description of the Related Art
A CDMA (Code Division Multiple Access) adaptive antenna receiving apparatus has been conventionally used for removal of interference caused by antenna directivity, as suggested in the following documents:
(A) Oh, Kohno and Imai, xe2x80x9cTDL Adaptive Array Antenna using diffusion gain for accomplishing spectrum diffusion multiple accessxe2x80x9d, Electronic Information Communication Academy, Vol. J75-BII, No. 11, pp. 815-825, 1992; and
(B) Tanaka, Miki and Sawahashi, xe2x80x9cCharacteristics of Judgment Feedback type Coherent Adaptive Diversity in DS-CDMAxe2x80x9d, Electronic Information Communication Academy, Radio Communication System Team Technical Report RC96-102, November 1996.
FIG. 1 is a block diagram of a conventional CDMA adaptive antenna receiving apparatus.
It is assumed that the illustrated CDMA adaptive antenna receiving apparatus includes N antennas wherein N is an integer equal to or greater than 2, and M multi-paths wherein M is an integer equal to or greater than 1, and is directed to a K-th user wherein K is an integer equal to or greater than 1.
With reference to FIG. 1, signals received at first to N-th antennas 110-1 to 110-N are divided to first to M-th paths in accordance with delay time, and input into both second to M-th delay units 120-2 to 120-M and first to M-th adaptive receivers 130-1 to 130-M. The delay units 120-2 to 120-M delay the input signals for synchronizing the input signals with the first path with respect to a timing. Thus, since the first delay unit 120-1 causes zero (0) delay, the first delay unit 120-1 is not illustrated in FIG. 1.
Output signals transmitted from the first to M-th adaptive receivers 130-1 to 130-M are added to one another in an adder 140, and the thus added output signals are inputted to a judge or evaluation circuit 150. The judge 150 transmits its output signal as a receipt symbol for the K-th user, which output signal is transmitted also to the first to M-th adaptive receivers 130-1 to 130-M.
Since the first to M-th adaptive receivers 130-1 to 130-M are designed to have the same structure, only the adaptive receiver for a m-th path (1xe2x89xa6mxe2x89xa6M) is illustrated in FIG. 2.
The received signals are diffused and demodulated in first to N-th reverse diffusion units 161-1 to 161-N, and thereafter, transmitted to both first to N-th multipliers 162-1 to 162-N and a delay unit 163. The received signals are multiplied with receipt weight in first to N-th multipliers 162-1 to 162-N. The signals having been multiplied with receipt weight are added to one another in an adder 164. Thus, the received signals are weighted.
The thus weighted signals are transmitted to a multiplier 165, a communication path estimating unit 166 and an adder 169. The communication path estimating unit 166 estimates deformation in communication paths. The deformation estimated by the communication path estimating unit 166 is transmitted to the multiplier 165 through a complex conjugate generating unit 167, and is multiplied with the weighted signals in the multiplier 165.
An output signal transmitted from the multiplier 165 defines a demodulated signal for the m-th path, and is transmitted to the adder 140 illustrated in FIG. 1.
The adder 140 adds output signals transmitted from the first to M-th adaptive receivers 130-1 to 130-M, to one another in RAKE synthesis, and transmits an output signal to the judge 150, which judges the signals with respect to data symbol.
In the adaptive receiver, an output signal transmitted from the judge 150 is multiplied with an output signal transmitted from the communication path estimating unit 166, in a multiplier 168, and then, input into the adder 169. The adder 169 calculates an error by subtracting an output transmitted from the adder 164, from an output transmitted from the multiplier 168, and transmits the thus calculated error to an adaptively updating unit 170.
The adaptively updating unit 170 updates receipt weight, based on the error transmitted from the adder 169 and a signal received at the antenna which signal is delayed by the delay unit 163 by a period of time necessary for demodulating the signal. Herein, there may be used a known algorithm such as least mean square algorithm, as an algorithm for adaptively updating receipt weight.
In the above-mentioned conventional adaptive antenna receiving apparatus, adaptive control is usually carried out by selecting a weight by which signals can be received regardless of signal-receipt conditions, as initial receipt weight, in order to make it possible to receive signals in any conditions, taking into consideration that signals come in different directions in dependence on signal-receipt conditions. For instance, a weight by which antenna directivity is non-directional is selected as such a weight. However, this causes a problem that it would take much time for receipt weight to converge to optimal receipt weight after receipt weight has been started to be adaptively updated.
Japanese Patent No. 2914445 (Japanese Unexamined Patent Publication No. 11-55216) has suggested the CDMA adaptive receiving apparatus including a weighting and synthesizing unit and a weight controller for one user. The weighting and synthesizing unit carries out weighting and synthesis for each of CDMA signals received in N antennas. The CDMA adaptive receiving apparatus further includes an error generator which (a) generates M error signals associated with each of paths for a desired wave signal, based on a communication path estimate and M demodulated signals which are demodulated at timings associated with M paths constituting a multi-path, based on signals transmitted from the weighting and synthesizing unit, and (b) synthesizes the error signals into one signal, which is to be transmitted to the weight controller.
Japanese Unexamined Patent Publication No. 10-341200 has suggested an adaptive array antenna receiving apparatus including a complex multiplying unit which multiplies received signals with a complex weight coefficient, an adder which adds output signals transmitted from the complex multiplying unit, to one another, a modulator which modulates known symbols, a subtracter which calculates a difference between an output signal transmitted from the adder and an output signal transmitted from the modulator, and a weight coefficient calculator which calculates the complex weight coefficient, based on the received signals and an output signal transmitted from the subtracter, only when known signal patterns in a desired station and an interference station are different from each other.
Japanese Unexamined Patent Publication No. 11-298388 has suggested an adaptive receiving apparatus including N antennas which receive signals multiplexed by a plurality of user signals, K adaptive receiving blocks associated with K users, which K adaptive receiving blocks form a directional pattern having a gain in any direction relative to the signals received at the antennas, and receive desired wave signals through a plurality of paths to thereby suppress interference wave signals, and a synthesizer which synthesizes a plurality of weight control errors with a user by means of path combination to thereby transmit a synthesized weight control error signal. Herein, N and K are integers both equal to or greater than 1. The adaptive receiving blocks form the directional pattern, based on the synthesized weight control error signal.
Japanese Unexamined Patent Publication No. 2000-22612 has suggested a CDMA type adaptive transceiver including a path searcher which extracts path level information and path delay time information out of signals received at antennas, M adaptive receivers which receive N signals having been received at the antennas, form a directional pattern having a gain in a direction of a desired wave signal every path delay time, and receives the desired wave signal to thereby suppress an interference wave signal, an antenna weight selector which selects antenna weights associated with L transmission paths out of M antenna weights, based on the path level information, L antenna weight controllers which determine transmission antenna weights defining a transmission directional pattern, based on an output signal transmitted from the antenna weight selector, and an adaptive transmitter which forms the transmission directional pattern having a gain in a user direction, by virtue of the transmission antenna weight transmitted from the antenna weight controllers, and transmits N antenna transmission signals used for transmitting the desired wave signal, wherein N is a positive integer, M is a positive integer, and L is an integer equal to or smaller than M.
The above-mentioned problem remain unsolved even in the above-mentioned Publications.
In view of the above-mentioned problems in the conventional adaptive antenna receiving apparatus, it is an object of the present invention to provide an adaptive antenna receiving apparatus which is capable of determining initial antenna receipt weight in accordance with signal-receiving conditions, and enhancing a convergence rate at which receipt weight is adaptively updated.
The adaptive antenna receiving apparatus in accordance with the present invention is characterized in that receipt weight is estimated before receipt weight is updated or during receipt weight is being updated, and determines the estimated receipt weight as initial receipt weight.
Specifically, there is provided an adaptive antenna receiving apparatus which receives signals at a plurality of antennas, multiplies each of the thus received signals with a weighting coefficient, and adds the products to one another to thereby detect the signals, including (a) an initial weighting coefficient calculator which calculates an initial weighting coefficient, based on the received signals, and (b) an adaptive receiver which updates the weighting coefficient in accordance with the received signals.
When the signals are comprised of a plurality of burst signals to be received at a certain interval, the initial weighting coefficient calculator may calculate the initial weighting coefficient for each of the burst signals, and the adaptive receiver may update the weighting coefficient in accordance with the received signals in the same burst signal.
There is further provided an adaptive antenna receiving apparatus including (a) a plurality of antennas, (b) a plurality of adaptive receivers each of which receives signals received in the antennas, in an adaptive antenna pattern in an order in which the signals arrived at the antennas, (c) a plurality of initial receipt weight calculators each of which calculates an initial antenna pattern for each of the signals, and outputs the thus calculated initial antenna pattern to each of the adaptive receivers, (d) an adder which adds output signals transmitted from each of the adaptive receivers, to one another, and (e) a judge which symbol-judges an output signal transmitted from the adder, and transmits an output signal to each of the adaptive receivers.
Each of the adaptive receivers may be comprised of (b1) a plurality of first multipliers each of which multiplies each of the received signals with a weighting coefficient, (b2) an adder which outputs transmitted from the first multipliers, to one another, (b3) a communication path estimating unit which estimates a communication path, based on an output signal transmitted from the adder, and outputs a first signal indicative of an estimated communication path, (b4) a second multiplier which multiplies an output signal transmitted from the judge, with the first signal, (b5) a subtracter which subtracts an output signal transmitted from the second multiplier, from an output signal transmitted from the adder, and (b6) an updating unit which adaptively calculates receipt weight, based on an output signal transmitted from the subtracter, a signal obtained by delaying the received signals, and initial receipt weight transmitted from each of the initial receipt weight calculators, each of the adaptive receivers controlling its receipt weight independently of other adaptive receivers.
Each of the initial receipt weight calculators may be comprised of (c1) a plurality of communication path estimating units each receiving each of signals received in the antennas, and (c2) a plurality of complex conjugate generators each receiving an output signal transmitted from each of the communication path estimating units, and wherein an output signal transmitted from each of the complex conjugate generators is transmitted to each of the adaptive receivers as an initial value for weight control to be made in each of the adaptive receivers.
Each of the initial receipt weight calculators may be comprised of (c1) a plurality of communication path estimating units each receiving each of signals received in the antennas, (c2) a direction estimating unit which estimates a direction in which a signal comes to the antennas, based on output signals transmitted from the communication path estimating units, and (c3) a receipt weight calculator which calculates receipt weight, based on output signals transmitted from the direction estimating unit, and wherein the receipt weight calculator transmits its output signal to each of the adaptive receivers in accordance with a signal transmitted from each of the delay detectors as an initial value for weight control to be made in each of the adaptive receivers.
There is still further provided a CDMA adaptive antenna receiving apparatus including (a) a plurality of antennas, (b) a plurality of adaptive receivers which receive signals received in the antennas, in an adaptive antenna pattern in an order in which the signals arrived at the antennas, (c) a plurality of initial receipt weight calculators each of which calculates an initial antenna pattern for each of the signals, and outputs the thus calculated initial antenna pattern to each of the adaptive receivers, (d) an adder which adds output signals transmitted from each of the adaptive receivers, to one another, and (e) a judge which symbol-judges an output signal transmitted from the adder, and transmits an output signal to each of the adaptive receivers.
In the CDMA adaptive antenna receiving apparatus, each of the adaptive receivers may be comprised of (b1) a plurality of reverse diffusion units each associated with each of the signals received in the antennas, (b2) a plurality of first multipliers each of which multiplies each of output signals transmitted from the reverse diffusion units, with a weighting coefficient, (b3) an adder which outputs transmitted from the first multipliers, to one another, (b4) a communication path estimating unit which estimates a communication path, based on an output signal transmitted from the adder, and outputs a first signal indicative of an estimated communication path, (b5) a second multiplier which multiplies an output signal transmitted from the judge, with the first signal, (b6) a subtracter which subtracts an output signal transmitted from the second multiplier, from an output signal transmitted from the adder, and (b7) an updating unit which adaptively calculates receipt weight, based on an output signal transmitted from the subtracter, signals obtained by delaying signals transmitted from the reverse diffusion units, and initial receipt weight transmitted from each of the initial receipt weight calculators, each of the adaptive receivers controlling its receipt weight independently of other adaptive receivers.
In the CDMA adaptive antenna receiving apparatus, each of the initial receipt weight calculators may be comprised of (c1) a plurality of reverse diffusion units each associated with each of the signals received in the antennas, (c2) a plurality of communication path estimating units each receiving an output signal transmitted from each of the reverse diffusion units, and (c3) a plurality of complex conjugate generators each receiving an output signal transmitted from each of the communication path estimating units, and wherein an output signal transmitted from each of the complex conjugate generators is transmitted to each of the adaptive receivers as an initial value for weighting control to be made in each of the adaptive receivers.
In the CDMA adaptive antenna receiving apparatus, each of the initial receipt weight calculators may be comprised of (c1) a plurality of reverse diffusion units each associated with each of the signals received in the antennas, (c2) a plurality of communication path estimating units each receiving an output signal transmitted from each of the reverse diffusion units, (c3) a direction estimating unit which estimates a direction in which a signal comes to the antennas, based on output signals transmitted from the communication path estimating units, and (c4) a receipt weight calculator which calculates receipt weight, based on output signals transmitted from the direction estimating unit, and wherein the receipt weight calculator transmits its output signal to each of the adaptive receivers as an initial value for weight control to be made in each of the adaptive receivers.
There is yet further provided an adaptive antenna receiving apparatus including (a) a plurality of antennas, (b) a plurality of adaptive receivers which receive signals received in the antennas, in an adaptive antenna pattern in an order in which the signals arrived at the antennas, (c) a plurality of initial receipt weight calculators each of which calculates initial receipt weight for adaptive control by means of the antenna pattern, and outputs the thus calculated initial receipt weight to each of the adaptive receivers, (d) a plurality of delay detectors each of which detects a directional difference between receipt weight calculated by each of the adaptive receivers and a direction in which the signals come to the antennas, estimated by the initial receipt weight calculators, and notifies each of the initial receipt weight calculators that the directional difference is over a predetermined directional difference threshold such that each of the initial receipt weight calculators transmits the initial receipt weight to each of the adaptive receivers, (e) an adder which adds output signals transmitted from each of the adaptive receivers, to one another, and (f) a judge which symbol-judges an output signal transmitted from the adder, and transmits an output signal to each of the adaptive receivers.
In the adaptive antenna receiving apparatus, each of the adaptive receivers may be comprised of (b1) a plurality of first multipliers each of which multiplies each of the received signals with a weighting coefficient, (b2) an adder which outputs transmitted from the first multipliers, to one another, (b3) a communication path estimating unit which estimates a communication path, based on an output signal transmitted from the adder, and outputs a first signal indicative of an estimated communication path, (b4) a second multiplier which multiplies an output signal transmitted from the judge, with the first signal, (b5) a subtracter which subtracts an output signal transmitted from the second multiplier, from an output signal transmitted from the adder, and (b6) an updating unit which calculates receipt weight, based on an output signal transmitted from the subtracter, a signal obtained by delaying the received signals, and the initial receipt weight, each of the adaptive receivers controlling its receipt weight independently of other adaptive receivers and outputting the controlled receipt weight to each of the delay detectors.
In the adaptive antenna receiving apparatus, each of the initial receipt weight calculators may be comprised of (c1) a plurality of communication path estimating units each receiving each of signals received in the antennas, (c2) a direction estimating unit which estimates a direction in which a signal comes to the antennas, based on output signals transmitted from the communication path estimating units, and (c3) a receipt weight calculator which calculates receipt weight, based on output signals transmitted from the direction estimating unit, and wherein the direction estimating unit transmits its output signal to the receipt weight calculator, and the receipt weight calculator transmits its output signal to each of the adaptive receivers in accordance with a signal transmitted from each of the delay detectors as initial value for weight control to be made in each of the adaptive receivers.
In the adaptive antenna receiving apparatus, each of the delay detectors may be comprised of (d1) a peak direction detector which detects a direction of maximum directivity of the receipt weight, based on receipt weight transmitted from the adaptive receivers, and (d2) a comparator which detects a difference in a peak direction between a direction transmitted from each of the initial receipt weight calculators and the direction of maximum directivity, and transmits a signal to the initial receipt weight calculators such that each of the initial receipt weight calculators transmits the initial receipt weight, when the difference is over a predetermined threshold difference.
There is still yet further provided a CDMA adaptive antenna receiving apparatus including (a) a plurality of antennas, (b) a plurality of adaptive receivers which receive signals received in the antennas, in an adaptive antenna pattern in an order in which the signals arrived at the antennas, (c) a plurality of initial receipt weight calculators each of which calculates initial receipt weight for adaptive control by means of the antenna pattern, and outputs the thus calculated initial receipt weight to each of the adaptive receivers, (d) a plurality of delay detectors each of which detects a directional difference between a weighting coefficient calculated by each of the adaptive receivers and a direction in which the signals come to the antennas, estimated by the initial receipt weight calculators, and notifies each of the initial receipt weight calculators that the directional difference is over a predetermined directional difference threshold such that each of the initial receipt weight calculators transmits the initial antenna pattern to each of the adaptive receivers, (e) an adder which adds output signals transmitted from each of the adaptive receivers, to one another, and (f) a judge which symbol-judges an output signal transmitted from the adder, and transmits an output signal to each of the adaptive receivers.
In the CDMA adaptive antenna receiving apparatus, each of the adaptive receivers may be comprised of (b1) a plurality of reverse diffusion units each associated with each of the signals received in the antennas, (b2) a plurality of first multipliers each of which multiplies each of output signals transmitted from the reverse diffusion units, with a weighting coefficient, (b3) an adder which outputs transmitted from the first multipliers, to one another, (b4) a communication path estimating unit which estimates a communication path, based on an output signal transmitted from the adder, and outputs a first signal indicative of an estimated communication path, (b5) a second multiplier which multiplies an output signal transmitted from the judge, with the first signal, (b6) a subtracter which subtracts an output signal transmitted from the second multiplier, from an output signal transmitted from the adder, and (b7) an updating unit which calculates receipt weight, based on an output signal transmitted from the subtracter, signals obtained by delaying signals transmitted from the reverse diffusion units, and the initial receipt weight transmitted from each of the initial receipt weight calculators, each of the adaptive receivers controlling its receipt weight independently of other adaptive receivers and outputting the controlled receipt weight to each of the delay detectors.
In the CDMA adaptive antenna receiving apparatus, each of the initial receipt weight calculators may be comprised of (c1) a plurality of reverse diffusion units each associated with each of the signals received in the antennas, (c2) a plurality of communication path estimating units each receiving an output signal transmitted from each of the reverse diffusion units, and (c3) a direction estimating unit which estimates a direction in which a signal comes to the antennas, based on output signals transmitted from the communication path estimating units, and (c4) a receipt weight calculator which calculates receipt weight, based on output signals transmitted from the direction estimating unit, the direction estimating unit transmitting its output signal to the receipt weight calculator, the receipt weight calculator transmits its output signal to each of the adaptive receivers in accordance with a signal transmitted from each of the delay detectors as an initial value for weight control to be made in each of the adaptive receivers.
In the CDMA adaptive antenna receiving apparatus, each of the delay detectors may be comprised of (d1) a peak direction detector which detects a direction of maximum directivity of the receipt weight, based on receipt weight transmitted from the adaptive receivers, and (d2) a comparator which detects a difference in a peak direction between a direction transmitted from each of the initial receipt weight calculators and the direction of maximum directivity, and transmits a signal to the initial receipt weight calculators such that each of the initial receipt weight calculators transmits the initial weight, when the difference is over a predetermined threshold difference.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
The first advantage is that it is possible to shorten a time necessary for receipt weight to converge. This is because that receipt weight which will accomplish in-phase synthesis is obtained before receipt weight is adaptively updated, and the thus obtained receipt weight is used as initial receipt weight for updating receipt weights.
The second advantage is that it is possible to prevent degradation in characteristics, caused by rapid change in a direction in which signals arrive at antennas. This is because that the adaptive antenna receiving apparatus in accordance with the present invention detects follow-up delay in adaptive control, caused by rapid change in a direction in which signals arrive at antennas, and presets receipt weight as optimal initial receipt weight.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.